The present invention relates to signal direction determining apparatus and, more particularly, to apparatus for providing an output indicative of the direction to a source of AC signals.
In the copending application of Raymond L. Barrett, Jr., Ser. No. 354,156, filed Mar. 5, 1982, for Randomized Tag to Portal Communication System, and assigned to the same assignee as the present application, there is described a system whereby the whereabouts of personnel in a hospital or other facility is determined and stored through the interaction of identification tags and portal interrogating stations. Each individual to be monitored is provided with a unique identification tag, and each portal is provided with an encircling magnetic loop and associated circuitry for establishing communication with any tags that come within range. As described in said application, the portals are provided with single loops and infer that each time a tag comes within range it passes through. Although physical constraints can be applied to doorways and passageways so as to minimize detection of a tag unless it is being carried through, the need for such constraint is undesirable and individuals do, on occasion, change their mind. Preferably, the system should be direction sensitive so as to recognize on which side of the portal a tag is located regardless of prior history.
It is, therefore, an object of the present invention to provide a practical and functional directional loop antenna array, and system therefor, whereby the direction to a signal source can be ascertained independent of the past history of such source.